Growth of vegetables is effected by absorbing nutrients comprising six principal elements, i.e., nitrogen, phosphoric acid, potassium, calcium, magnesium, sulfur and a small quantity of iron, manganese etc. from the root, wherein such nourishment is absorbed in the form of ionized inorganic materials.
In soil cultivation, a fertilizer including much organic materials such as an oil cake, as compost is applied, wherein such fertilizer can not be absorbed as the nutrients until the fertilizer is dissolved by bacteria etc. in the soil and converted into inorganic material little by little.
In view of this point a, water cultivation is a reasonable method in which a suitable amount of synthetic inorganic chemical fertilizer is introduced in the water. Water cultivation has many other advantages hereinafter described, particularly for vegetables unsuitable for consecutive planting. Vegetables which grow very poorly when planted consecutively can not be cultivated if the soil is not changed each time of cultivation or the cultivation position is not changed, while water cultivation can be performed repeatedly in the same position by changing the water in the vessel without troublesome work, such as position changing or soil changing.
There are many causes of vegetables being unsuitable for consecutive planting. The most important factor among these is a self-poisoning phenomenon caused by an organic secretion of the vegetable itself and putrefaction of the remaining root etc. That is to say, existence of the organic substance is harmful to the growth of the vegetable. In case of soil cultivation, the consecutive cultivation can not be performed until the organic substance is dissolved and disappears.
The water cultivation method is epoch-making as a new agricultural method and is expected to develop in the future. The principal features of the water cultivation method are as follows:
1. Minimizing of power and mechanization can be effected. That is to say, labor with a hoe, a spade and the like is not necessary, furthermore labor for weeding and the like is not necessary. Such labor is replaced by a computational control such as water quality control or environment control which is light work.
2. In order to eliminate hindrances of consecutive planting, change of soil or change of farming location is not necessary, and cultivation can be effected at the same location repeatedly by changing the water only. While improvement of breeding or grafting has been performed in order to eliminate obstruction according to consecutive planting up to now, the environment becomes changeable so as to be optimum for vegetables.
3. Since fertilizer is dissolved and circulated in the water, loss of the fertilizer does not result from flowing and the necessary nourishment can be applied effectively in the required amount.
4. Stable cultivation can be performed substantially without being influenced by weather conditions.
5. Automation by means of computational control is possible and each vegetable can be cultivated at optimum conditions, therefore both quality and production amount are stabilized throughout the year.
6. The root portion, the most important part of the vegetable is satisfied with the necessary conditions of water, air, nourishing liquid (hereinafter nourishing water) and is separated from, natural environment, therefore damage by blight and insects is scarcely produced, so as to permit clarified cultivation.
7. On account of controlled cultivation, planting is highly developed and intensive; therefore the harvest amount per unit area can be increased several times greater than that attainable using soil cultivation.
On the other hand, conventional water cultivation has the following defects:
1. Since the water is circulated for the cultivation, if disease germs are introduced in the water, the germs spread throughout and the damage is large.
2. The most important point of water cultivation is in the quality of the nourishing water, therefore water cultivation in a region of bad water quality is difficult.
3. Even in the case of good water quality, the water is contaminated at the end step of harvest causing it to be diseased.
4. When remaining roots and leaves are rotted in the water cultivation vessel, elevation of BOD (Biochemical Oxygen Demand) obstructs growth of vegetables.
Although water cultivation has the above described defects, in the conventional water cultivation method the organic substance dissolved in the nourishing water can not be effectively eliminated, therefore the water quality can not be held at optimum condition. Moreover, for specific vegetables, such as horseradishes, which can grow up only in restricted natural environment, the water cultivation can not be carried out on a business scale, because the water quality of the nourishing water can not be held in suitable condition for growing horseradishes.
The inventors have noticed that activated carbon adsorbs an organic substance quite easily but does not adsorb an ionized inorganic substance, and the present invention can eliminate the above four defects which obstruct the development of the water cultivation method. That is to say, we have noticed that the property of activated carbon of adsorbing organic substance dissolved in the nourishing water corresponds to elimination of BOD (Biochemical Oxygen Demand) and COD (Chemical Oxygen Demand) in the water utilizing the activated carbon for processing the waste water.
The principal object of the present invention is to provide an improved method of water cultivation by using an activated carbon as a nourishing water clarifying medium so as to hold the water quality constant, wherein growth promotion and harvest increase of vegetables are effected to a degree which can not be expected in conventional water cultivation method moreover, water cultivation can be applied to usual vegetables as well as specific vegetables such as horseradishes which grow up only under specific environmental conditions.